1. Field of the Invention
The invention relates to a milling tool, particularly a thread milling cutter.
2. Description of the Prior Art
Milling tools are generally known and are used in the most varied constructional forms for carrying out different milling tasks. Milling methods are subdivided on the basis of the surface produced, the tool shape and the kinematics, inter alia into plain, circular, profile and form milling, as well as hobbing. Profile milling e.g. includes the milling of threads or grooves.
In thread milling the tool rotates about its own axis and simultaneously moves in three axes, namely the space axes x, y and z. The most important setting parameters are the milling cutter speed and the feed rate of the milling cutter in the xy-plane.
In the case of milling tools it is known to place milling inserts radially with respect to the rotation axis. The milling inserts can be screwed or soldered to the tool.
DE 36 32 296 A1 discloses a thread milling tool for milling internal or external threads on workpieces. The thread milling tool has a milling cutter shank, to which is fixed a trapezoidal turning milling plate, which is provided with a toothed thread milling edge on both plate sides. The thread milling edges are formed by the two plate sides and an edge face at an angle thereto.
The problem of the invention is to provide a milling tool of the aforementioned type, which can be used in stable, universal form and which in particular permits a high cutting capacity, even in the case of a small tool diameter.
According to the invention the problem is solved by the features of claim 1. The bearing and orientation surfaces of the milling tool are consequently constructed for a substantially tangential reception of milling inserts, e.g. turning cutting bits or indexable inserts. A comparison with a conventional milling tool, where the milling inserts are positioned radially on the circumference of the cutter shank and are e.g. fixed by screws or wedges with the milling tool according to the invention shows that for the same diameter of the two shanks on the milling tool according to the invention it is possible to provide more milling inserts on the milling tool according to the invention than with a conventional milling tool. Thus, the milling tool according to the invention can be equipped with a plurality of milling inserts. This is achieved by the tangential reception of the milling inserts. The milling capacity, i.e. the metal removal rate per time unit or revolution of such a milling tool is higher than conventional milling tools, so that the tool lifes also longer.
In the case of conventional milling tools the receptacles for the milling inserts are often constructed in such a way that on the circumference of the milling tool there are deep reception openings oriented radially to the milling cutter rotation axis, which reduces the tool stability. In the case of the milling tool according to the invention, this situation does not arise. Therefore the milling tool according to the invention is more stable and compact than conventional milling tools, particularly when compared with a conventional tool with in each case the same number of fixed milling inserts.
In particularly preferred manner in the case of the milling tool according to the invention, the bearing and orientation surfaces of the milling insert and milling tool engage with one another and are pressed together under pretension. The force acting on the milling insert when machining a workpiece consequently does not act directly on the fastening elements of the milling inserts and is instead transferred to the bearing and orientation surfaces, where transmission occurs by frictional grip. In conventional milling tools this force acts on the fastening elements, e.g. screws or soldered joints. There is a high risk of loosening or breaks on the fastening elements, e.g. the shearing off of screws, etc. In the milling tool according to the invention this risk is much lower as a result of the advantageous force transfer to the bearing and orientation surfaces.
In conventional milling inserts, which are e.g. radially fixed by screws, the accuracy to size when machining workpieces is very highly dependent on the fixing of the inserts in the milling tool. A change to the fixing position has a direct effect on the depth of cut of the cutting edge of the milling insert. Therefore the groove, thread, etc. produced on the workpiece no longer has a uniform depth. With the milling tool according to the invention a change in the fixing position of the milling insert in the milling tool acts approximately tangentially and there is a reduced change to the cutting-in depth of the milling insert.
It is possible to provide several receptacles on one circumferential surface of the milling tool. The circumferential surface is formed by equally large portions, preferably by the receptacles themselves. The receptacles can be arranged in one or more planes of the milling tool, preferably in closely juxtaposed form to one another. Thus, two or more receptacles can be successively positioned coaxially to the rotational milling axis. The successive receptacles can be aligned or displaced with respect to one another. Although the receptacles could be arranged irregularly around the rotational milling axis, they are preferably positioned regularly and in particular axially symmetrically to the rotational milling axis, so that the milling tool is completely symmetrical. Therefore the milling tool rotates and the rotational movement of the milling tool is not impaired by imbalances due to irregularly positioned milling inserts. The receptacles can be closely juxtaposed on the circumferential surface and are preferably adjacent to one another. This utilizes the entire circumferential surface of the milling tool as a receptacle. The receptacles are consequently individual portions of the circumferential surface of the milling tool. The milling tool can have a reception area with a polygonal cross-section. The cross-section can e.g. be a square or an equilateral hexagon or octagon. The portions constructed as receptacles could consequently all be the same size.
The bearing and orientation surfaces of the milling tool receptacle can be positioned in an inclined manner and in particular at an angle to one another. It is possible for one bearing and orientation surface of a receptacle to be more strongly inclined, e.g. forming a larger angle with the horizontal, than its facing bearing and orientation surface. The receptacle has bearing and orientation surfaces, as well as support surfaces, which are constructed in different planes. The support surfaces, as well as the bearing and orientation surfaces preferably form a right angle. The bearing and orientation surfaces are in particular flanks on the receptacle. The receptacle can be constructed in truncated trapezoidal manner, but can also have other geometries. The receptacles are preferably recesses in the milling cutter shank. However, they can also be separate parts fixable to the said shank.
The receptacles of the milling tool preferably have holes with the aid of which the milling insert can be fixed to the milling tool. It is possible to use two holes for fixing a tool insert. The holes are located on a common plane oriented coaxially to the rotational milling axis. In the case of several milling inserts on the milling tool, the holes can be axially symmetrical to the rotational milling axis. The center axes of the holes can be perpendicular to the rotational milling axis.
The milling insert is eccentrically braced in order to bring about a positive bearing of the bearing and orientation surfaces of the milling insert on the bearing and orientation surfaces of the milling tool. As a result the bearing and orientation surfaces in each case automatically engage with one another on tightly screwing down the insert. The eccentric bracing can be brought about by a spot facing of the holding section of the milling insert and/or a sloping head of a joining element, particularly a screw. The holes in the tool are at a somewhat shorter distance from the bearing and orientation surfaces of the tool than in the case of the corresponding elements of the insert. Thus, on tightening, the screws push the insert into its receptacle.
The milling cutter shank can have two areas, namely a reception area and a holding area. The receptacles for the milling inserts are preferably located on the reception area. The holding area can be used for introducing the milling tool into a milling machine. It is also possible to use shankless milling tools, e.g. hobbing cutters. They can be fixed to the milling machine by means of a hole, e.g. by means of a central hole passing through the entire milling tool body.
In a particularly preferred arrangement, the milling insert has a holding section and a cutting section. The holding section can be plate-like. The optionally profiled cutting edges of the milling insert are located on the cutting section. The cutting edge can extend over only a portion or over the entire width of the cutting section. Preferably the holding section and cutting section are arranged at an angle to one another. The angle is obtuse and is in the range 100xc2x0 to 150xc2x0. The bearing and orientation surfaces of the milling insert are preferably constructed on the holding section. On equipping the milling tool with the milling inserts only the holding section engages on the bearing surface of the receptacle and the cutting section is free from holding functions.
The milling insert, particularly the cutting section of the milling insert, can have a tool face, which can be straight or rounded. The tool face can be constructed in chip guidance face form. In particular the preferably crescent-shaped tool face located in the milling tool rotation direction can be used for chip removal. The chips can be moved past the adjacent, preferably aligned, trailing edge of the closest milling insert.
It is possible to construct the milling insert with chamfered edges directed towards a workpiece to be machined. This is in particular used with milling inserts having large dimensions in order to prevent any contact between said edges and the workpiece.
The milling tool, as well as the milling insert are preferably made from metal, e.g. carbide or high speed steel, but can also be made from other materials usable for milling purposes.
These and further features can be gathered from the claims, description and drawings and the individual features, both singly and in the form of subcombinations, can be implemented in an embodiment of the invention and in other fields and can represent advantageous, independently protectable constructions, for which protection is here claimed. The subdivision of the application into individual sections and the subheadings in no way limit the general validity of the statements made thereunder.